Sorry that the problem description was not sufficient. Here is a self-contained code replicating the problem:
require(doBy) x <- as.data.frame(matrix(ncol=3,seq(1,12),dimnames=list(c(),c("hh","total","total.inf")))) summaryBy(total+total.inf~hh,x,FUN=sum) What surprises me are the zeros in the resulting total.sum column. The problem remains if total.inf is renamed to totalinf or total_inf but not if renamed to ttotal.inf . Can anyone explain to me what the rules for naming columns are so that I can avoid such mistakes in the future? Thanks a lot! ________ ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.